The present invention relates to diagnostic kits for determining the presence of one or more analytes in a fluid sample. More particularly, the present invention relates to a dermal concentration patch for increasing the concentration of an analyte expressed through the skin to a conveniently measurable level.
The determination of a patient's physiological status is frequently assisted by chemical analysis for the existence and/or concentration of predetermined chemical species in a body fluid. These tests, which are typically conducted in the physician's office or in the hospital, may be characterized by their collection technique as invasive, such as analyses of blood, or non-invasive, such as analyses of urine and perspiration.
Blood is frequently analyzed for a wide variety of components, and clinical laboratories are generally equipped with instrumentation which can provide a highly quantitative profile of the blood's composition. However, blood collection is inherently invasive, and therefore attended by several disadvantages. Analyses based upon collection of a sample of blood are generally restricted to the physician's office or clinical laboratory, which reduces convenience for ambulatory patients and greatly increases cost. In addition, some risks associated with an invasive procedure can range from undesirable at best to unacceptable, depending upon the condition of the patient, and the nature and necessity of the test desired to be performed.
Many analytes or metabolites of interest can additionally be detected in urine, which is characterized by its predictable supply and non-invasive collection. However, as will become apparent, urine analysis is not well suited for use in the principal intended application of the concentration patch of the present invention.
Perspiration is, under certain circumstances, an ideal body fluid for analysis in the determination of physiological status. Its non-invasive collection renders it suitable for use out of the physician's office, and its similarity to blood in terms of its content of biological molecules renders it suitable for a wide range of physiological testing.
Thus, a variety of diagnostic kits for monitoring an analyte in sweat have been developed. For example, U.S. Pat. No. 3,552,929 to Fields, et al. discloses a bandaid-type test patch particularly suited for determining the chloride ion concentration in perspiration as a method of diagnosing cystic fibrosis. The apparatus disclosed in Fields comprises an absorptive sweat collecting pad with an impermeable overlying layer for the purpose of preventing evaporation. When the absorptive pad is saturated, the patch is removed from the skin and exposed to a series of strips impregnated with incremental quantities of silver chromate or silver nitrate, the color of which undergoes a well known change upon conversion to the chloride salt.
U.S. Pat. No. 4,706,676 to Peck discloses a dermal collection device which comprises a binder to prevent reverse migration of an analyte, a liquid transfer medium which permits transfer of an analyte from the dermal surface to the binder, and an occlusive cover across the top of the liquid transfer medium and binder.
Peck discloses application of the dermal collection patch in the detection of human exposure to various environmental chemicals. After the dermal collection device has been worn on a patient's skin for a period of time, the patch is removed for analysis. Analysis requires chemically separating the bound substance of interest from the binding reservoir and thereafter undertaking qualitative and/or quantitative measurement by conventional laboratory techniques.
The prior art generally suffers from one or more important limitations when convenient field use of a diagnostic test patch is desired. In particular, prior art diagnostic test patches are generally only useful for determining the presence of analytes such as halide ions, which are present in sweat in relatively high concentrations. Other prior art dermal patches are merely collection devices from which the analytes must later be separated and concentrated or otherwise prepared for analysis in accordance with known laboratory techniques. In addition, the occlusive outer layer type devices of the prior art are susceptible to the problem of back diffusion of perspiration and/or analytes contained therein.
Thus, there remains a need in many diverse applications for a method and apparatus for the noninvasive determination of a preselected analyte in a body fluid such as perspiration, which can be utilized to detect the presence of low-concentration analytes in perspiration without the need for conventional instrumentation. The test kit should be low-cost and suitable for convenient use by non-medical personnel.